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United States Geological Survey: Staff Publications

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Articles 901 - 930 of 1026

Full-Text Articles in Earth Sciences

Bridge Scour Data Management, Mark N. Landers Jan 1992

Bridge Scour Data Management, Mark N. Landers

United States Geological Survey: Staff Publications

A Bridge Scour Data Management System has been developed by the U.S. Geological Survey to support preparation, compilation, and analysis of bridge scour measurement data. Users may interactively store, retrieve, select, update, and display bridge scour and associated data. Interactive processing makes use of full-screen menus and form fill-ins, and an instruction window. Optional help and limits windows provide additional information for each of about 150 items in the data set for each bridge-scour site. The data set items include all of the essential information from a detailed scour measurement. Each data set has four categories of information: site data; …

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First- And Second-Order Patterns Of Stress In The Lithosphere: The World Stress Map Project, Mary Lou Zoback Jan 1992

First- And Second-Order Patterns Of Stress In The Lithosphere: The World Stress Map Project, Mary Lou Zoback

United States Geological Survey: Staff Publications

To date, more than 7300 in situ stress orientations have been compiled as part of the World Stress Map project. Of these, over 4400 are considered reliable tectonic stress indicators, recording horizontal stress orientations to within < ±25 °. Remarkably good correlation is observed between stress orientations deduced from in situ stress measurements and geologic observations made in the upper 1-2 km, well bore breakouts extending to 4-5 km depth and earthquake focal mechanisms to depths of-20 km. Regionally uniform stress orientations and relative magnitudes permit definition of broad-scale regional stress patterns often extending 20-200 times the approximately 20-25 km thickness of the upper brittle lithosphere. The "first-order" midplate stress fields are believed to be largely the result of compressional forces applied at plate boundaries, primarily ridge push and continental collision. The orientation of the intraplate stress field is thus largely controlled by the geometry of the plate boundaries. There is no evidence of large lateral stress gradients (as evidenced by lateral variations in stress regime) which would be expected across large plates if simple resistive or driving basal drag tractions (parallel or antiparallel to absolute motion) controlled the intraplate stress field. Intraplate areas of active extension are generally associated with regions of high topography: western U.S. Cordillera, high Andes, Tibetan plateau, western Indian Ocean plateau. Buoyancy stresses related to crustal thickening and/or lithospheric thinning in these regions dominate the intraplate compressional stress field due to plate-driving forces. These buoyancy forces are just one of several categories of "second-order" stresses, or local perturbations, that can be identified once the first-order stress patterns are recognized. These second-order stress fields can often be associated with specific geologic or tectonic features, for example, lithospheric flexure, lateral strength contrasts, as well as the lateral density contrasts which give rise to buoyancy forces. These second-order stress patterns typically have wavelengths ranging from 5 to 10+ times the thickness of the brittle upper lithosphere. A two-dimensional analysis of the amount of rotation of regional horizontal stress orientations due to a superimposed local stress constrains the ratio of the magnitude of the horizontal regional stress differences to the local uniaxial stress. For a detectable rotation of 15 °, the local horizontal uniaxial stress must be at least twice the magnitude of the regional horizontal stress differences. Examples of local rotations of SHmax orientations include a 750-85 ° rotation on the
northeastern Canadian continental shelf possibly related to margin-normal extension derived from sediment-loading flexural stresses, a 50 °-60 ° rotation within the East African rift relative to western Africa due to extensional buoyancy forces caused by lithospheric thinning, and an approximately 90 ° rotation along the northern margin of the Paleozoic Amazonas rift in central Brazil. …

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A Reconnaissance Study Of Herbicides And Their Metabolites In Surface Water Of The Midwestern United States Using Immunoassay And Gas Chromatography/Mass Spectrometry, E. Michael Thurman, Donald A. Goolsby, Michael Meyer, Margaret Mills, Michael L. Pomes, Dana W. Kolpin Jan 1992

A Reconnaissance Study Of Herbicides And Their Metabolites In Surface Water Of The Midwestern United States Using Immunoassay And Gas Chromatography/Mass Spectrometry, E. Michael Thurman, Donald A. Goolsby, Michael Meyer, Margaret Mills, Michael L. Pomes, Dana W. Kolpin

United States Geological Survey: Staff Publications

Preemergent herbicides and their metabolites, particularly atrazine, deethylatrazine, and metolachlor, persisted from 1989 to 1990 in the majority of rivers and streams in the midwestern United States. In spring, after the application of herbicides, the concentrations of atrazine, alachlor, and simazine were frequently 3-10 times greater than the U.S. Environmental Protection Agency maximum contaminant level (MCL). The concentration of herbicides exceeded the MCLs both singly and in combination. Two major degradation products of atrazine (deisopropylatrazine and deethylatrazine) also were found in many of the streams. The order of persistence of the herbicides and their metabolites in surface water was atrazine …

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In Situ Stress Measurements To 3.5 Km Depth In The Cajon Pass Scientific Research Borehole: Implications For The Mechanics Of Crustal Faulting, Mark D. Zoback, John H. Healy Jan 1992

In Situ Stress Measurements To 3.5 Km Depth In The Cajon Pass Scientific Research Borehole: Implications For The Mechanics Of Crustal Faulting, Mark D. Zoback, John H. Healy

United States Geological Survey: Staff Publications

Measurements of in situ stress orientation and magnitude at the site of the Cajon Pass research borehole have been made from depths of 0.9-3.5 km using the hydraulic fracturing technique and analysis of stress-induced well bore breakouts. The results of these measurements support two important conclusions about the mechanics of crustal faulting. First, the magnitudes of measured in situ stresses indicate ratios of shear to normal stress. on favorably oriented fault planes that are consistent with predictions based on Mohr-Coulomb theory and laboratory-determined coefficients of friction in the range of 0.6-1.0 assuming hydrostatic pore pressure (this is commonly known as …

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Numerical Methods 101 - Convergence Of Numerical Models, David B. Thompson Jan 1992

Numerical Methods 101 - Convergence Of Numerical Models, David B. Thompson

United States Geological Survey: Staff Publications

A numerical model is convergent if and only if a sequence of model solutions with increasingly refined solution domains approaches a fixed value. Furthermore, a numerical model is consistent only if this sequence converges to the solution of the continuous equations which govern the physical phenomenon being modeled. Given that a model is consistent, it is insufficient to apply it to a problem without testing for sensitivity to the size of the time and distance steps which form the discrete approximation of the solution domain. That is, convergence testing is a required component of any modeling study.

Two models were …

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Modeling Flow And Flood-Plain Storage In A Tidally Affected River, A. G. Strickland, Jerad D. Bales Jan 1992

Modeling Flow And Flood-Plain Storage In A Tidally Affected River, A. G. Strickland, Jerad D. Bales

United States Geological Survey: Staff Publications

A one-dimensional, unsteady-flow model was calibrated, validated, and tested for a 30.4-mile reach of the tidally affected Roanoke River, North Carolina. The model includes a storage reservoir to represent the two-dimensional processes associated with flood-plain storage and release in the one-dimensional flow model. Simulated and measured water levels differed by less than 0.5 foot, and the average absolute difference between simulated and measured flows was 7 percent.

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United States Geological Survey Bridge Scour Evaluation Program In Texas, David D. Dunn, Henry R. Hejl Jr. Jan 1992

United States Geological Survey Bridge Scour Evaluation Program In Texas, David D. Dunn, Henry R. Hejl Jr.

United States Geological Survey: Staff Publications

The Federal Highway Administration has mandated that all bridges in the Federal Aid System crossing over water be evaluated for scour susceptibility. The United States Geological Survey and the Texas Department of Transportation (TXDOT) have initiated a multi-year, multi-phase program to develop scour evaluation and analysis procedures that will allow TXDOT to quickly and efficiently evaluate some 11,000 bridges crossing over water in the state.

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Usgs Urban Stonnwater Investigations In The Dallas-Fort Worth, Texas Metroplex, R. Brad Jennings, Tim H. Raines, Lucia G. Colangione Jan 1992

Usgs Urban Stonnwater Investigations In The Dallas-Fort Worth, Texas Metroplex, R. Brad Jennings, Tim H. Raines, Lucia G. Colangione

United States Geological Survey: Staff Publications

Stormwater runoff in urban and industrialized areas carries a considerable amount of pollutants to nearby lakes and streams. In an effort to control this source of pollution, the U.S. Environmental Protection Agency has issued stormwater regulations to control these discharges. Municipalities with a population of 100,000 or more must undertake a process to obtain permits to control the quality of their storm runoff. The Dallas-Fort Worth metroplex includes seven cities that must meet these regulations and obtain permits. The U.S. Geological Survey is assisting the North Texas Council of Governments and its associated cities in meeting the water science requirements …

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Flux Of Metals Between Sediment And The Water Column, N. S. Simon, K. O. Dennen Jan 1992

Flux Of Metals Between Sediment And The Water Column, N. S. Simon, K. O. Dennen

United States Geological Survey: Staff Publications

The role of nitrogen-containing compounds in the flux of metals between sediment and the overlying water column is discussed.

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Stress-Strain Relation In Debris Flow Analysis, Chi-Hai Ling, Cheng-Lung Chen, Chyan-Deng Jan Jan 1992

Stress-Strain Relation In Debris Flow Analysis, Chi-Hai Ling, Cheng-Lung Chen, Chyan-Deng Jan

United States Geological Survey: Staff Publications

In debris flow analysis, the generalized viscop1astic fluid (GVF) model can be used as the constitutive equations. When the yield stress is negligible, the shear expression in the GVF model for simple shear flow reduces to r = µ1 (du/dz)n, where r is the shear stress, µ1 is the consistency index, du/dz is the shear rate, and n is the flow behavior index. In this paper the r versus du/dz relation is studied by running experiments with 14 mm dry glass spheres in a conveyor-belt flume. A comparison of the estimated r with the measured du/dz …

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Sr-Isotope Record Of Quaternary Marine Terraces On The California Coast And Off Hawaii, Kenneth R. Ludwig, Daniel R. Muhs, Kathleen R. Simmons, James G. Moore Jan 1992

Sr-Isotope Record Of Quaternary Marine Terraces On The California Coast And Off Hawaii, Kenneth R. Ludwig, Daniel R. Muhs, Kathleen R. Simmons, James G. Moore

United States Geological Survey: Staff Publications

Strontium-isotopic ratios of dated corals have been obtained from submerged reefs formed during Quaternary glacial periods off the Hawaiian islands. These data, combined with data from deep-sea sediments, tightly constrain the secular variation of marine 87Sr/86Sr for the past 800,000 yr. Although long-term trends are apparent, no significant (>0.02‰), rapid (<100,000 yr) excursions in 87Sr/86Sr were resolved nor did we observe any samples with 87Sr/86Sr greater than that of modern seawater. Strontium in mollusks from elevated marine terraces formed during interglacial periods on the southern California coast show resolvable and consistent variations in …

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The Last Interglacial-Glacial Transition In North America: Evidence From Uranium-Series Dating Of Coastal Deposits, Daniel R. Muhs Jan 1992

The Last Interglacial-Glacial Transition In North America: Evidence From Uranium-Series Dating Of Coastal Deposits, Daniel R. Muhs

United States Geological Survey: Staff Publications

Considerable uncertainty exists as to whether the last interglacial was relatively "short" (~10 ka) or "long" (-20-60 ka), although most investigators generally agree that the last interglacial correlates with all or part of deep-sea oxygen-isotope stage 5. A compilation of reliable U-series ages of marine terrace corals from deposits that have been correlated with isotope stage 5 indicates that there were three relatively high sea-level stands at ca 125-120 ka, ca. 105 ka, and ca. 85-80 ka, and these ages agree with the times of high sea level predicted by the Milankovitch orbital-forcing theory. At a number of localities, however, …

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Stable Isotope Study Of Water-Rock Interaction And Ore Formation, Bayhorse Base And Precious Metal District, Idaho, Robert R. Seal Ii, Robert O. Rye Jan 1992

Stable Isotope Study Of Water-Rock Interaction And Ore Formation, Bayhorse Base And Precious Metal District, Idaho, Robert R. Seal Ii, Robert O. Rye

United States Geological Survey: Staff Publications

The Bayhorse base and precious metal district situated east of the Idaho batholiths in south-central Idaho. The ores occur near the Nevada Mountain granitic stock as veins cutting the lower Paleozoic Ramshorn Slate and the Garden Creek Phyllite, and as fillings around breccias fragments within the Bayhorse Dolomite. The veins are dominated by siderite and tetrahedrite, with lesser quartz and galena, whereas the breccias ores dominantly comprise only quartz and galena. Mineralization and intrusive activity were contemporaneous during Cretaceous time. Fluid inclusion and stable isotope data indicate that mineralization formed from hot (ca. 375° -225°C), CO2-rich (≤8.3 ± …

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Superambient Heat Capacities Of Synthetic Stibnite, Berthierite, And Chalcostibite: Revised Thermodynamic Properties And Implications For Phase Equilibria, Robert R. Seal Ii, Richard A. Robie, Paul B. Barton Jr., Bruce Hemingway Jan 1992

Superambient Heat Capacities Of Synthetic Stibnite, Berthierite, And Chalcostibite: Revised Thermodynamic Properties And Implications For Phase Equilibria, Robert R. Seal Ii, Richard A. Robie, Paul B. Barton Jr., Bruce Hemingway

United States Geological Survey: Staff Publications

Stibnite (Sb2S3), berthierite (FeSb2S4), and chalcostibite (CuSbS2) are important antimony-bearing minerals. Stibnite is the main ore mineral of antimony and occurs as an important accessory in many epigenetic ore deposits, especially in later stages of deposition or in peripheral facies of mineralization. Berthierite is a common accessory mineral in antimony deposits. Its occurrence, particularly in gold-antimony deposits, has received considerable scientific attention. Furthermore, stibnite, berthierite, and chalcostibite represent important reference phases for understanding phase equilibria in more complex systems, such as those containing tetrahedrite-tennantite solid solutions.

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Residence Times In River Basins As Determined By Analysis Of Long-Term Tritium Records, Robert L. Michel Jan 1992

Residence Times In River Basins As Determined By Analysis Of Long-Term Tritium Records, Robert L. Michel

United States Geological Survey: Staff Publications

The US Geological Survey has maintained a network of stations to collect samples for the measurement of tritium concentrations in precipitation and streamflow since the early 1960s. Tritium data from outflow waters of river basins draining 4500-75 000 km2 are used to determine average residence times of water within the basins. The basins studied are the Colorado River above Cisco, Utah: the Kissimmee River above Lake Okeechobee, Florida; the Mississippi River above Anoka, Minnesota; the Neuse River above Streets Ferry Bridge near Vanceboro, North Carolina; the Potomac River above Point of Rocks. Maryland; the Sacramento River above Sacramento, California: …

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Introduction To Special Section On The Cajon Pass Scientific Drilling Project, Mark D. Zoback, Arthur H. Lachenbruch Jan 1992

Introduction To Special Section On The Cajon Pass Scientific Drilling Project, Mark D. Zoback, Arthur H. Lachenbruch

United States Geological Survey: Staff Publications

Over the past few decades a generally accepted conceptual model for the thermomechanics of the San Andreas fault was based on three factors believed to have been supported by observation: (1) maximum horizontal shear stress increases with depth in the crust at the rate of 7-8 MPa/km (as indicated by measurements in relatively shallow boreholes), roughly the same rate of shear stress increase as in other regions [e.g., McGarr et al., 1982], (2) the maximum horizontal stress direction in the vicinity of the fault was oriented at about 300-45 ° to its strike (as indicated by the predominance of right-lateral …

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Stress Field Constraints On Intraplate Seismicity In Eastern North America, Mary Lou Zoback Jan 1992

Stress Field Constraints On Intraplate Seismicity In Eastern North America, Mary Lou Zoback

United States Geological Survey: Staff Publications

Focal mechanisms of 32 North American midplate earthquakes (mb = 3.8-6.5) were evaluated to determine if slip is compatible with a broad-scale regional stress field derived from plate-driving forces and, if so, under what conditions (stress regime, pore pressure, and frictional coefficient). Using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes ( ± 10 °), the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative …

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A Brief Literature Review Of Open-Channel Current Meter Testing, Kirk G. Thibodeaux Jan 1992

A Brief Literature Review Of Open-Channel Current Meter Testing, Kirk G. Thibodeaux

United States Geological Survey: Staff Publications

The U.S. Geological Survey (USGS) has undertaken the task of conducting an evaluation of the USGS's standard water-flow current meter, the Price type-AA current meter. The first part of the USGS's task was to conduct a comprehensive literature review to determine the extent and types of testing that has been conducted to evaluate the performance of various types of current meters used for open-channel flow measurements. The meter types included in the review were the vertical-axis mechanical type, the horizontal-axis mechanical type, the electromagnetic type, and the point-velocity acoustic (ultrasonic) type current meters. The review revealed that current meters have …

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Topographic Effects On Stormflow Acidity, David Wolock Jan 1992

Topographic Effects On Stormflow Acidity, David Wolock

United States Geological Survey: Staff Publications

This paper describes the theoretical and observed effects of topography on stormflow acidity in upland, forested watersheds. The theoretical effects were determined by a sensitivity analysis using the hydrologic model TOPMODEL. The observed effects were determined by an analysis of topographic and stormflow acidity data collected from eight watersheds in Wales, Great Britain. Results of the analyses indicated that the observed effects of topography were consistent with the theoretical expectations; that is, topography has an important effect on flow path, and that flow path, in turn, has an effect on stormflow acidity.

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Incorporating Hydraulic Structures In An Open-Channel Model, Eric D. Swain Jan 1992

Incorporating Hydraulic Structures In An Open-Channel Model, Eric D. Swain

United States Geological Survey: Staff Publications

The open-channel flow model, BRANCH, is a routinely used numerical tool for modeling rivers, canals, and waterway networks. Although a simplified hydraulic structure representation is included in the model, no universal subroutine that can represent hydraulic structures by their rating curve equations has been included in the BRANCH model.

Accordingly, a subroutine has been developed that specifies flow through a structure by a stage-discharge relation. The structure flow equation is used to generate coefficients in the solution matrix that represent the structure in the same computational format as the open-channel flow equations. Field applications have shown that this new subroutine …

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Network Applications Of The Usgs Branch Model, Raymond W. Schaffranek Jan 1992

Network Applications Of The Usgs Branch Model, Raymond W. Schaffranek

United States Geological Survey: Staff Publications

Applications of a numerical model for simulating unsteady flow in dendritic or interconnected open-channel networks are presented to demonstrate the model's potential for addressing environmental problems and formulating engineering decisions in water-resources investigations. The model is computationally robust and readily adaptable to a broad spectrum of hydraulic conditions and open-channel configurations. The four-point, implicit, finite difference model has been implemented on numerous open-channel reaches and networks in support of various water-resources investigations conducted within the U.S. Geological Survey. In this paper, network applications of the model to a residential canal system in Cape Coral, Florida; to a distributary system of …

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U And Sr Isotopes In Ground Water And Calcite, Yucca Mountain, Nevada: Evidence Against Upwelling Water, J. S. Stuckless, Z. E. Peterman, Daniel R. Muhs Jan 1991

U And Sr Isotopes In Ground Water And Calcite, Yucca Mountain, Nevada: Evidence Against Upwelling Water, J. S. Stuckless, Z. E. Peterman, Daniel R. Muhs

United States Geological Survey: Staff Publications

Hydrogenic calcite and opaline silica deposits in fault zones at Yucca Mountain, Nevada, have created considerable public and scientific controversy because of the possible development of a high-level nuclear waste repository at this location. Strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep-seated waters. The vein deposits are isotopically distinct from ground water in the two aquifers that underlie Yucca Mountain, indicating that the calcite could not have precipitated from ground water. The data are consistent with a surficial origin for the hydrogenic deposits.

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Additional Fossil Evidence On The Differentiation Of The Earliest Euprimates, Kenneth D. Rose, Thomas M. Bown Jan 1991

Additional Fossil Evidence On The Differentiation Of The Earliest Euprimates, Kenneth D. Rose, Thomas M. Bown

United States Geological Survey: Staff Publications

Several well-preserved jaws of the rare North American omomyid primate Steinius vespertinus, including the first known antemolar dentitions, have been discovered in 1989 and 1990 in the early Eocene Willwood Formation of the Bighorn Basin, Wyoming. They indicate that its dental formula is as primitive as those in early Eocene Donrussellia (Adapidae) and Teilhardina (Omomyidae) - widely considered to be the most primitive known euprimates - and that in various dental characters Steinius is as primitive or more so than Teilhardina. Therefore, despite its occurrence at least 2 million years later than Teilhardina, S. vespertinus is the …

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Early Eocene Biotic And Climatic Change In Interior Western North America, Scott L. Wing, Thomas M. Bown, John D. Obradovich Jan 1991

Early Eocene Biotic And Climatic Change In Interior Western North America, Scott L. Wing, Thomas M. Bown, John D. Obradovich

United States Geological Survey: Staff Publications

Imprecise correlation of the marine and terrestrial fossil records has been a major obstacle to understanding migration and extinction of continental biotas and early Cenozoic climate change

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The Pangaean Megamonsoon- Evidence From The Upper Triassic Chinle Formation, Colorado Plateau, Russell F. Dubiel, Judith Totman Parrish, J. Michael Parrish, Steven C. Good Jan 1991

The Pangaean Megamonsoon- Evidence From The Upper Triassic Chinle Formation, Colorado Plateau, Russell F. Dubiel, Judith Totman Parrish, J. Michael Parrish, Steven C. Good

United States Geological Survey: Staff Publications

The Upper Triassic Chinle Formation was deposited at an exceptional time in Earth's paleogeographic and paleoclimatic history. During the Triassic, the supercontinent Pangaea was at its greatest size, in terms of both aggregated continental crust and exposed land area. Moreover, the exposed land was divided symmetrically about the paleoequator between the northern and south- ern hemispheres. These conditions were ideal for maximizing monsoonal circulation, as predicted from paleoclimate models. The Chinle was deposited between about 5° to 15° N paleolatitude in the western equatorial region of Pangaea, a key area for documenting the effects of the monsoonal climate. This study …

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The October 17, 1989, Loma Prieta, California, Earthquake And Its Aftershocks: Geometry Of The Sequence From High-Resolution Locations, Lynn D. Dietz, William L. Ellsworth Jan 1990

The October 17, 1989, Loma Prieta, California, Earthquake And Its Aftershocks: Geometry Of The Sequence From High-Resolution Locations, Lynn D. Dietz, William L. Ellsworth

United States Geological Survey: Staff Publications

Hypocenters of the Loma Prieta sequence form a dipping zone that rises from the mainshock hypocenter and is parallel to the mainshock nodal plane. Most aftershocks cluster around the perimeter of the zone, surrounding a relatively aseismic center which approximates the region of mainshock rapture. At its southeastern end, the dipping aftershock zone warps into a vertical surface that corresponds to the San Andreas fault. In the central and northwestern parts of the zone at depths above -10 km, the aftershocks define numerous disjoint fault structures. The large component of reverse-slip observed in this event agrees with a simple model …

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Coseismic Stress Changes Induced By The 1989 Loma Prieta, California Earthquake, Andrew J. Michael, William L. Ellsworth, David H. Oppenheimer Jan 1990

Coseismic Stress Changes Induced By The 1989 Loma Prieta, California Earthquake, Andrew J. Michael, William L. Ellsworth, David H. Oppenheimer

United States Geological Survey: Staff Publications

Earthquake focal mechanisms from before and after the 1989 Loma Prieta, California earthquake are used to infer the coseismic stress change. Before the main shock, most earthquakes correspond to right lateral slip on planes sub-parallel to the San Andreas fault, and imply a generally N-S most compressionsal stress axis anda vertical intermediate stress axis. Aftershocks within the main shock rupture zone, however, display almost every style and orientation of faulting, implying an extremely heterogeneous stress field. This suggests that the main shock relieved most, if not all, of the shear stress acting on its fault plane. Aftershocks that lie on …

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Sedimentary Paleoenvironments Of Fossil Platyrrhine Localities, Miocene Pinturas Formation, Santa Cruz Province, Argentina, Thomas Bown, Claudio N. Larriestra Jan 1990

Sedimentary Paleoenvironments Of Fossil Platyrrhine Localities, Miocene Pinturas Formation, Santa Cruz Province, Argentina, Thomas Bown, Claudio N. Larriestra

United States Geological Survey: Staff Publications

The Pinturas Formation is a pyroclastic and epiclastic aeolian deposit of Miocene age lying discordantly upon Jurassic rocks in the elevated Andean precordillera of northwest Santa Cruz Province, Argentina. The history of de\'elopment of the Pinturas Formation was significantly affected by the gradual, though sporadic, draping of this aeolian sediment across a profound, slowly filling paleotopography. The Pinturas depositional cycle consisted of: (1) minor aeolian deposition followed by soil formation, and (2) major aeolian deposition followed by intervals of regional erosion. Fluvial action seems to have been almost wholly confined to intraformational erosion, and two significant intraformational erosional unconformities divide …

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Phytoplankton Dynamics In Three Rocky Mountain Lakes, Colorado, U.S.A., Diane M. Mcknight, Richard L. Smith, J. Platt Bradbury, Jill S. Baron, Sarah Spaulding Jan 1990

Phytoplankton Dynamics In Three Rocky Mountain Lakes, Colorado, U.S.A., Diane M. Mcknight, Richard L. Smith, J. Platt Bradbury, Jill S. Baron, Sarah Spaulding

United States Geological Survey: Staff Publications

In 1984 and 1985 seasonal changes in phytoplankton were studied in a system of three lakes in Loch Vale, Rocky Mountain National Park, Colorado. Three periods were evident: (1) A spring bloom, during snowmelt, of the planktonic diatom Asterionella Formosa, (2) a mid- summer period of minimal algal abundance, and (3) a fall bloom of the blue-green alga Oscillatoria limnetica. Seasonal phytoplankton dynamics in these lakes are controlled partially by the rapid flushing rate during snowmelt and the transport of phytoplankton from the highest lake to the lower lakes by the stream, Icy Brook. During snowmelt, the A. …

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Crustal Strain Near The Big Bend Of The San Andreas Fault: Analysis Of The Los Padres-Tehachapi Trilateration Networks, California, Donna Eberhart-Phillips, Michael Lisowski, Mark D. Zoback Jan 1990

Crustal Strain Near The Big Bend Of The San Andreas Fault: Analysis Of The Los Padres-Tehachapi Trilateration Networks, California, Donna Eberhart-Phillips, Michael Lisowski, Mark D. Zoback

United States Geological Survey: Staff Publications

In the region of the Los Padres-Tehachapi geodetic network, the San Andreas fault (SAF) changes its orientation by over 30 ° from N40 °W, close to that predicted by plate motion for a transform boundary, to N73 °W. The strain orientation near the SAF is consistent with right-lateral shear along the fault, with maximum shear rate of 0.38 ± 0.01 μrad/yr at N63 °W. In contrast, away from the SAF the strain orientations on both sides of the fault are consistent with the plate motion direction, with maximum shear rate of 0.19 ± 0.01 μrad/yr at N44 °W. The strain …

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